Q.

A capacitor is charged by a battery. The battery is removed and another identical uncharged capacitor is connected in parallel. The total electrostatic energy of resulting system   [2017]

1 decreases by a factor of 2  
2 remains the same  
3 increases by a factor of 2  
4 increases by a factor of 4  

Ans.

(1)

When the capacitor is charged by a battery of potential V, then energy stored in the capacitor, 

Ui=12CV2                                          ...(i)

When the battery is removed and another identical uncharged capacitor is connected in parallel

Common potential, V'=CVC+C=V2

Then the energy stored in the capacitor,

Uf=12(2C)(V2)2=14CV2                                        ...(ii)

   From eqns. (i) and (ii), Uf=Ui2

It means the total electrostatic energy of resulting system will decrease by a factor of 2.